http://www.startrek.com/article/10-things-we-learned-about-discovery  

Mary Chieffo and Kenneth Mitchell, who play the Klingons L’Rell and
Kol, are super-serious about learning the Klingon language. The two
actors noted that they work closely with *** Robyn Stewart ***, the
show’s Klingon expert, and Rea Nolan, the show's linguist, to fully
learn the language. They practice dialogue during the three hours in
their makeup chairs. The goal is not only to speak it perfectly, but
to read – and understand every word – of the Klingon in their
scripts.